Along an assembly line, diapers and various types of other absorbent articles may be assembled by adding components to and otherwise modifying an advancing, continuous web of material. For example, in some processes, advancing webs of material are combined with other advancing webs of material. In other examples, individual components created from advancing webs of material are combined with advancing webs of material, which in turn, are then combined with other advancing webs of material. Once the desired component parts are assembled, the advancing web(s) and component parts are subjected to a final knife cut to separate the web(s) into discrete diapers or other absorbent articles. The discrete diapers or absorbent articles may also then be folded and packaged.
For purposes of web control and/or monitoring purposes, absorbent article converting lines may utilize various types of sensor technology to obtain various types of inspection data relating to continuous webs and discrete components added to the webs along the converting line as absorbent articles are constructed therefrom. Example sensor technology may include vision systems, photoelectric sensors, proximity sensors, laser or sonic distance detectors, and the like. Sensor data may be communicated to a controller in various ways. In turn, the controller may be programmed to receive sensor data and report and/or store such data as well as make adjustments to manufacturing processes.
In some manufacturing processes, illuminating optical systems and cameras are arranged adjacent converting lines in order to communicate data to the controller relating to surface topographies of advancing webs and components. In some optical systems, a light source may be used to illuminate a surface of an advancing substrate, wherein light reflected from the substrate is detected by a camera. The light emitted from the light source may also be linearly polarized such that the camera can ascertain information relating to surface features of the substrate by detecting polarized and depolarized light reflected from the substrate surface. Although such optical systems that rely on the detection of reflected polarized light may be able to detect certain anomalies on substrates having relatively smooth surfaces, these systems may not work as well with substrates having relatively rough surfaces, such as nonwovens. In addition, optical systems that rely on detecting polarized light reflected from a substrate surface may not be well suited to detect through holes in substrates, because at acute angles light would not pass through holes due to either the caliper of the substrate or height deviations caused by wrinkles or web flutter; or at perpendicular angles, light from such systems would merely pass through the holes rather than being reflected, confusing holes with surface features which scatter or absorb light such as bond patterns, graphics, or non-uniform basis weights or particulates. As such, some systems utilized to detect through holes in substrates may be configured to illuminate a surface of a substrate and detect light passing through holes in the substrate. Thus, the systems may rely on the detection of relatively bright light as an indication of a through hole in a substrate. However, such systems may have difficulties in detecting through holes in relatively thin and/or translucent material as light traveling through the holes and the substrate may both appear relatively bright, making it hard to discern the existence, locations, and/or perimeters of the holes.
Consequently, it would be beneficial to configure and utilize optical inspection systems that are able to detect and track the locations of through holes in continuous substrates or discrete substrates that may be advancing at relatively high production speeds.